Two-dimensional (2D) electronic materials are of considerable interest due to their potential applications in future electronics. A common example is graphene, a thin organic 2D material with in-plane it-conjugation. Although graphene exhibits exceptional charge mobility and mechanical stability, its use in semiconductor-based devices is limited by its zero bandgap. Dimensional reduction and chemical functionalization can increase the bandgap, rendering graphene semiconducting, but such methods generally reduce its charge mobility and can introduce numerous defects. This has led to a sustained effort towards identifying 2D materials with intrinsic non-zero bandgaps that could replace conventional semiconductors. Two other broad classes of materials have been investigated: the layered metal chalcogenides (e.g., MoS2, WSe2) and 2D covalent-organic frameworks (COFs). The former can be deposited as large-area single sheets in a “top-down” approach. They have been shown to perform well in device testing, but do not easily lend themselves to chemical functionalization and tunability. In contrast, COFs generally are prepared by “bottom-up” solution-based synthetic methods.
While COFs are attractive because they are subject to rational modification, the electronic properties of COFs are largely inferior to metal chalcogenides because the functional groups used to connect their building blocks typically do not allow in-plane conjugation.
Accordingly, improved compositions and methods are needed.